The present invention relates to a lens barrel with a variable magnification optical system that has a plurality of lens groups through which a ray of a photographic object passes, and changes magnification by moving prescribed lens groups.
Cameras each carrying a camera lens (hereinafter referred to also as a zoom lens) having a variable focal length have so far been on the market. In each of these zoom lenses, a focal length thereof is changed when plural lens groups constituting the optical system of the zoom lens are moved so that a distance between the zoom lenses may be changed.
A method to move plural lens groups to be in parallel with an optical axis is roughly divided into two types; one of them is one wherein a cam cylinder on which a cam groove is formed and a cam pin that engages with the cam groove are formed on the outer circumference of a lens frame, and the lens frame is engaged with a straightforward guide, and the lens frame is moved straight when the cam cylinder is rotated, and the other is one wherein a shaft is arranged to be substantially in parallel with an optical axis to be a guide shaft for a straightforward guide, and a sleeve on which the guide shaft penetrates through the lens frame is formed, thus, the lens frame is caused by a stepping motor and a lead screw to slide along the guide shaft directly, for its straightforward movement.
The latter one stated above employing the guide shaft arranged to be mostly in parallel with an optical axis is used frequently for the photographing optical system of a camera that requires no degeneracy, because it can be of a simple structure, requiring neither cam cylinder in a complicated cam shape nor a complicated structure of lens barrel.
There is disclosed a structure wherein the one employing the guide shaft arranged to be substantially in parallel with an optical axis is applied to a light-reflecting optical system, two lens groups are moved by two motors, and a movement of an engagement member that engages with a lead screw of the motor on one side is transmitted to the lens group on the finder side (for example, see Patent Document 1). This Patent Document 1 discloses a structure of a lens barrel of the light-reflecting optical system.
[Patent Document 1] JP-A 2003-222946 (FIG. 2-FIG. 6)
A zoom lens has therein a plurality of lens groups, and is arranged so that prescribed lens groups among them move on an optical axis in its direction to change a focal length, and it is general that an allowable error of an optical axis deviation between respective lens groups in these plural lens groups varies depending on an individual lens group constituting the zoom lens.
In recent years, there is carried out the so-called center-aligning wherein a lens frame is formed so that a lens may be moved in the direction perpendicular to its optical axis, and an optical axis of a certain lens group and that of another lens group facing the aforesaid lens group can be aligned highly accurately by moving the lens for fine adjustment on the lens frame, without relying on parts accuracy of the lens and the lens frame holding the lens. Owing to this center-aligning, a problem of decentering has been dissolved, making it possible to obtain a camera lens with stable performance that causes no individual difference on an image taken by the camera lens.
On the other hand, in the structure of a lens barrel of a light-reflecting optical system described in the Patent Document 1 stated above, the lens barrel is divided into a barrel member that includes a reflection member for light-reflecting optical system and includes a fixed lens group on the subject side and a box-shaped barrel member that is arranged behind the aforesaid barrel member and includes both movable lens groups and fixed lens group.
In the case of this structure of a lens barrel, a guide shaft is incorporated in the box-shaped barrel member under the condition that all lens groups engaging with the guide shaft are incorporated. Therefore, it is impossible to select specific lens groups from movable lens groups and fixed lens groups which are arranged behind for aligning optical axes more accurately, and to conduct center-aligning for specific lens groups. In addition, there is no space for inserting a jig for moving a lens for fine adjustment when conducting center-aligning, resulting in a problem that the box-shaped barrel member interposes an obstacle in the course of center-aligning.